The present invention relates to motion picture film duplicating equipment and, in particular, to a detector for determining if image-bearing film being copied is in-frame with the unexposed film onto which it is being copied.
Motion picture film is commonly duplicated on equipment known as step optical printers. Such printers are available commercially, for example, from the Oxberry Division of Richmark Camera, Inc., Carlstadt, New Jersey and a common model is known as the Oxberry Model 1500. The printer consists of a projector, a camera, and a common drive mechanism for both the projector and camera.
The projector consists of a feed reel, a takeup reel, and a shuttle-gate along with a transport which feeds developed film from the feed reel to the takeup reel through the shuttle-gate. The gate consists of a mechanism which transfers the film on a frame-by-frame basis from the film transport to a projecting position, holds each frame at the projecting position in registration while it is illuminated and photographed and then returns the film to the transport for its eventual travel to the takeup reel.
The camera similarly consists of a feed reel containing a supply of unexposed film, a takeup reel for the film after exposure and a shuttle-gate. The camera also includes an appropriate shutter system and transport mechanism which feeds unexposed film to the camera gate. The unexposed film is then lifted from the transport mechanism, held in position and exposed through the shutter to a projected image which comprises the frame of film in the projector shuttle-gate. The camera gate mechanism then returns the exposed film to the transport mechanism where it is transported to the takeup reel for subsequent development and processing.
Both the projector and camera are driven by a common drive mechanism which operates continuously. The function of the gate is thus to stop each frame of the continuously moving developed and unexposed films to permit the image on the developed film to be exposed to the unexposed film. To make a proper duplicate of the developed film, the unexposed film must be exposed on a frame-by-frame basis properly registered to the developed film.
In actual practice, a very serious problem develops during operation of the printer. For any one of several reasons, film in either the projector or camera can fall out of synchronization with film in the other. This may occur in the projector, for example, as a result of an improper splice, a misaligned sprocket hole, or film that was slightly mutiliated during handling. While the problem could also occur in the camera, this is a rather infrequent occurence since the film loaded into the camera is virgin film that is made under strict quality control procedures. However, occasionally, the unexposed film in the camera also sometimes falls out of synchronization because of some malfunction or irregularity. As a result of film falling out of synchronization, the section of film presented in the projector (or camera) gate is not a true frame. It may, for example, comprise the bottom portion of one frame along with the top portion of the next frame. If the equipment were permitted to run in such an out-of-frame condition, the result is that useless information would be exposed on the camera film. The problem is compounded by the fact that the printer operates automatically so that unless an out-of-frame condition is detected and corrected promptly, as much as 2,000 feet of film could be wasted. The problem is compounded even further by the fact that the exposed film could be developed, printed and projected before the problem was discovered.
On 35 mm film, the sprocket hold spacing is such that each frame spans four sprocket holes. thus, if for any reason at all, the gate does not contain a length of film with the four sprocket holes making up a full frame, the information photographed is worthless. On smaller format films, there is a closer relationship between the sprocket holes and frames and a slipped sprocket hole could result in an entire frame being lost on the copy.
In view of the above, it is the principal object of the present invention to provide an out-of-frame detector for use with a step optical printer which readily detects an out-of-frame condition and alerts the operator of the printer of such condition.
A further object is to provide a detector which responds quickly to an out-of-frame situation so as to minimize the amount of film that could be wasted as a result of such condition.
A still further object is to provide such a detector which may readily be incorporated into existing printers at a nominal cost and with relative ease.